Magnetoresisitive sensor and manufacturing method therefor

ABSTRACT

A magnetoresistive sensor fabricated by creating first antiferromagnetic layers on the upper surfaces of a lower-gap layer, the antiferromagnetic layer having first and second exposed portions separated by a track width formed by the upper surface of the lower-gap layer. Then, a free magnetic layer, a nonmagnetic electrically conductive layer, a pinned magnetic layer and a second antiferromagnetic layer are stacked on the first antiferromagnetic layers and a portion on the track width one after another. Since the free magnetic layer is created after the first antiferromagnetic layer, the free magnetic layer and the first antiferromagnetic layer are adhered to each other with a high degree of reliability. When the direction of magnetization in the free magnetic layer is changed by an external magnetic field, the electrical resistance of the magnetoresistive sensor also changes. The change in electrical resistance is, in turn, used for detecting the external magnetic field. Since the first antiferromagnetic layers put the free magnetic layer in a single-domain state in the X direction, the amount of Barkhausen noise can be reduced.

BACKGROUND OF THE INVENTION

1. Field of the Invention

In general, the present invention relates to a magnetoresistive sensormounted on a magnetic recording/reproducing apparatus or anothermagnetic detecting apparatus. In particular, the present inventionrelates to a magnetoresistive sensor and its manufacturing method,wherein the magnetoresistive sensor is of the so-called spin-valve type,and wherein the electrical resistance thereof varies due to a change inrelation between the direction of the magnetization of a pinned magneticlayer and the direction of magnetization of a free magnetic layer whichis affected by an external magnetic field.

2. Description of the Related Art

FIG. 3 is a diagram showing a front view of a magnetoresistive sensorbased on the spin-valve effect disclosed in U.S. Pat. No. 5,206,590. TheZ direction in the figure is the moving direction of a magneticrecording medium such as a rigid disk relative to the magnetoresistivesensor whereas the Y direction is the direction of a leaking magneticfield (an external magnetic field) from the magnetic recording medium.

In the magnetoresistive sensor shown in FIG. 3, a nonmagnetic underlayer2 made of a nonmagnetic material such as Ta (tantalum) is created on alower-gap layer 1 made of typically Al₂O₃ (aluminum oxide). A freemagnetic layer 3 is created on the nonmagnetic underlayer 2. Anonmagnetic electrically conductive layer 5, a pinned magnetic layer 6and a second antiferromagnetic layer 7 are stacked on the free magneticlayer 3 with a predetermined width in the X direction one after anotherin the order they are enumerated. At (i) portions on both edges of thenonmagnetic electrically conductive material 5 and the pinned magneticmaterial 6, first antiferromagnetic layers 4 are created on the freemagnetic layer 3.

An upper layer 8 made of a nonmagnetic material such as Ta is created onthe first antiferromagnetic layers 4 on both the sides and on the secondantiferromagnetic layer 7 in the middle. Lead layers (electricallyconductive layers) 9 are created on the upper layer 8, sandwiching anopen track width Tw.

An exchange anisotropic coupling on a film boundary surface between thefirst antiferromagnetic layer 4 and the free magnetic layer 3 puts thefree magnetic layer 3 into a single-domain state in the X direction,orientating the directions of magnetization in the X direction. On theother hand, an exchange anisotropic coupling on a film boundary surfacebetween the second antiferromagnetic layer 7 and the pinned magneticlayer 6 puts the pinned magnetic layer 6 into a single-domain state inthe Y direction, fixing the directions of magnetization in the Ydirection (a direction perpendicular to the surface of the paper towardthe reader).

In the magnetoresistive sensor based on the spin-valve effect, asteady-state current is supplied from the lead layer 9 to the freemagnetic layer 3, the nonmagnetic electrically conductive layer 5 andthe pinned magnetic layer 6 in the X direction. When a leaking magneticfield (an external magnetic field) from a magnetic recording medium suchas a rigid disk is provided in the Y direction, the direction ofmagnetization of the free magnetic layer 3 changes from the X directionto the Y direction. The change in relation between the direction ofmagnetization in the free magnetic layer 3 and the pinned direction ofmagnetization of the pinned magnetic layer 6, which change is caused bya variation in magnetization direction in the free magnetic layer 3,changes the electrical resistance. The change in electrical resistanceresults in a change in voltage which is used for detecting the leakingmagnetic field from the magnetic recording medium.

As described above, in the magnetoresistive sensor shown in FIG. 3, theexchange anisotropic couplings on the film boundary surface between thefirst antiferromagnetic layer 4 and the free magnetic layer 3 and on thefilm boundary surface between the second antiferromagnetic field 7 andthe pinned magnetic layer 6 orientate the magnetic directions of thefree magnetic layer 3 and the pinned magnetic layer 6 respectively indirections perpendicular to each other. As a result, the amount ofBarkhausen noise can be reduced, giving rise to a merit that a linearresponse characteristic of the change in electrical resistance withrespect to the leaking magnetic field from the magnetic recording mediumcan be reliably obtained. In addition, since the dimension of the pinnedmagnetic layer 6 in the X direction is fixed, the off-track performancewith respect to the magnetic recording medium is also good.

In a process of manufacturing a magnetoresistive sensor with a structureshown in FIG. 3, however, after the nonmagnetic electrically conductivelayer 5, the pinned magnetic layer 6 and the second antiferromagneticlayer 7 are formed on the free magnetic layer 3 using sputter processes,it is necessary to remove the nonmagnetic electrically conductive layer5, the pinned magnetic layer 6 and the second antiferromagnetic layer 7from the (i) portions using an etching process such as ion milling. Inaddition, also required is a process for creating the firstantiferromagnetic layer 4 on the (i) portions at both edges of thesecond antiferromagnetic layer 7, the pinned magnetic layer 6 and thenonmagnetic electrically conductive layer 5 each with a fixed dimensionin the X direction.

The film thickness of each layer in the magnetoresistive sensor has avalue ranging from several tens of Angstroms to several hundreds ofAngstroms. The film thickness of the nonmagnetic electrically conductivelayer 5 is about several tens of Angstroms. It is extremely difficult toremove the stacked structure comprising the three layers, that is, thenonmagnetic electrically conductive layer 5, the pinned magnetic layer 6and the second antiferromagnetic layer 7, each having such a very smallfilm thickness by means of ion milling with a high degree of accuracy.From the technological point of view, at the portion (i), it is alsodifficult to remove only the nonmagnetic electrically conductive layer 5without removing the free magnetic layer 3 in order to expose the freemagnetic layer 3. If a portion of the free magnetic layer 3 isinadvertently removed in this etching process, the magneticcharacteristic of the free magnetic layer 3 will be adversely affected.If the nonmagnetic electrically conductive layer 5 is inadvertently leftat the portion (i) on the surface of the free magnetic layer 3, on theother hand, the first antiferromagnetic layer 4 created on the freemagnetic layer 3 is not closely adhered to the free magnetic layer 3because of the residual nonmagnetic electrically conductive layer 5. Asa result, no exchange anisotropic coupling is generated on the filmboundary surface between the first antiferromagnetic layer 4 and thefree magnetic layer 3.

SUMMARY OF THE INVENTION

The present invention addresses the problems of the conventionalmagnetoresistive sensor described above. It is thus an object of thepresent invention to provide a magnetoresistive sensor and itsmanufacturing method wherein an antiferromagnetic layer is broughtdirectly in contact with a free magnetic layer in such a way that theformer is closely adhered to the latter with a high degree ofreliability and each layer of the magnetoresistive sensor can be createdwith ease.

The magnetoresistive sensor provided by the present invention comprisesa free magnetic layer, a nonmagnetic electrically conductive formed onthe free magnetic layer, and a pinned magnetic layer formed on thenonmagnetic electrically conductive layer, an antiferromagnetic layerfor orientating the directions of magnetization of the free magneticlayer by an exchange anisotropic coupling on the film boundary surfacebetween the two layers, and a pinning layer for pinning the directionsof magnetization of the pinned magnetic layer in a direction crossingthe direction of magnetization of the free magnetic layer, wherein theelectrical resistance of the magnetoresistive sensor changes when thedirection of magnetization of the free magnetic layer changes due to anexternal magnetic field. The magnetoresistive sensor is characterized inthat the antiferromagnetic layer is placed beneath the free magneticlayer and includes first and second portions separated by apredetermined track width, and the fist and second portions of theantiferromagnetic layer and the free magnetic layer are closely adheredto each other.

It is possible to design the following configurations (a) and (b) in themagnetoresistive sensor provided by the present invention.

(a) Parts of portions on both sides of the lower-gap layer are removedin order to form a predetermined track width. The antiferromagneticlayer portions are then provided in the removed parts. Subsequently, thefree magnetic layer is created on the upper surfaces of theantiferromagnetic layers on both sides and the upper surface of aportion on the formed track width between the antiferromagnetic layers.

(b) The antiferromagnetic layer is created on the entire upper surfaceof the lower-gap layer and a nonmagnetic underlayer having a dimensionequal to a predetermined track width is then created on theantiferromagnetic layer. The free magnetic layer is then created on theupper surfaces of the antiferromagnetic layer and the nonmagneticunderlayer.

In addition, the antiferromagnetic layer which forms an exchangeanisotropic coupling on the film boundary surface between the layer andthe free magnetic layer is typically made of a material such as α—Fe₂O₃(iron oxide), NiO (nickel oxide), an Ni—Mn (nickel-manganese) alloy or aPt—Mn (platinum-manganese) alloy.

A method of manufacturing the magnetoresistive sensor with theconfiguration (a) described above is characterized in that the methodcomprises: removing parts of portions on both sides on the surface ofthe lower-gap layer to form a predetermined track width; creatingantiferromagnetic layers in the removed parts of the portions on bothsides on the lower-gap layer; stacking a free magnetic layer, anonmagnetic electrically conductive layer and a pinned magnetic layerone after another on the antiferromagnetic layers on both sides and anonmagnetic underlayer on the lower-gap layer between theantiferromagnetic layers; and creating a pinning layer for fixing thedirections of magnetization of the pinned magnetic layer in a directioncrossing the direction of magnetization of the free magnetic layer.

A method of manufacturing the magnetoresistive sensor with theconfiguration (b) described above is characterized in that the methodcomprises: creating an antiferromagnetic layer on the entire surface ofa lower-gap layer and a nonmagnetic underlayer on the antiferromagneticlayer; removing the nonmagnetic underlayer to form a predetermined trackwidth and exposing said antiferromagnetic layer on both sides; stackinga free magnetic layer, a nonmagnetic electrically conductive layer and apinned magnetic layer one after another on the upper surface of theantiferromagnetic layers exposed on both the sides of the nonmagneticlayer and on the upper surface of the nonmagnetic layer; and creating apinning layer for pinning the directions of magnetization of the pinnedmagnetic layer in a direction crossing the direction of magnetization ofthe free magnetic layer.

In this present invention, unlike the conventional magnetoresistivesensor shown in FIG. 3, the antiferromagnetic layer for orientating thedirection of magnetization of the free magnetic layer is created beneaththe free magnetic layer. It is thus not necessary to remove both theedges of the nonmagnetic electrically conductive layer and the pinnedmagnetic layer created on the free magnetic layer, making themanufacturing of the magnetoresistive sensor provided by the presentinvention very simple. In addition, the free magnetic layer can beclosely adhered to the antiferromagnetic layer, making it possible toorientate the direction of magnetization of the free magnetic layer witha high degree of reliability.

In addition, α—Fe₂O₃,NiO, the Ni—Mn alloy or the Pt—Mn alloy used formaking the antiferromagnetic layer is a corrosion-proof material.Accordingly, when the antiferromagnetic layer is created first and thefree magnetic layer is then created on the antiferromagnetic material,since the surface of the antiferromagnetic layer is corrosion proof, theantiferromagnetic material and the free magnetic material createdthereon can be closely adhered to each other. As a result, it ispossible to display an exchange anisotropic coupling on the filmboundary surface between the two layers.

By the same token, in the method of manufacturing the magnetoresistivesensor provided by the present invention, it is not necessary to etchthe nonmagnetic electrically conductive layer, the pinned magnetic layerand the pinning layer for pinning the direction of magnetization of thepinned magnetic layer. As a result, the processes of manufacturing thelayers become very simple.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a front view of a magnetoresistive sensorprovided by the present invention;

FIG. 2 is a diagram showing a front view of another magnetoresistivesensor provided by the present invention; and

FIG. 3 is a diagram showing a front view of the conventionalmagnetoresistive sensor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a diagram showing a front view of a magnetoresistive sensorprovided by the present invention and FIG. 2 is a diagram showing afront view of a magnetoresistive sensor provided by the presentinvention with a structure different from that of the magnetoresistivesensor shown in FIG. 1. Both of these magnetoresistive sensors are bothbased on the spin-valve effect.

In the magnetoresistive sensors shown in FIGS. 1 and 2, the Z directionis the movement direction of a magnetic recording medium and the Ydirection is the direction of a leaking magnetic field (externalmagnetic field) from the magnetic recording medium.

First of all, the structure of the magnetoresistive sensor shown in FIG.1 is explained. As shown in the figure, a lower-gap undivided layer 1 ofthe magnetoresistive sensor is made of Al₂O₃ (aluminum oxide) andincludes first and second etched (removed) portions separated by acentrally-located un-etched (remaining) portion. A firstantiferromagnetic layer 10 is formed over the lower-gap layer 1 andetched such that first and second portions of the antiferromagneticportion are located in the first and second etched portions of thelower-gap layer 1, and are separated by a predetermined track width Tw.Then, a free magnetic layer 3 is formed which includes first and secondsections respectively formed on upper surfaces of the first and secondportions of the antiferromagnetic layer 10, and includes a third sectionwhich extends on or over the upper surface of the lower-gap portion 1located between the first and second portions of the antiferromagneticlayer 10. (The third section is formed on the lower-gap portion 1 when anonmagnetic underlayer 2, shown in FIG. 1, is omitted.) The freemagnetic layer 3 is made of an Ni—Fe (nickel-iron) alloy.

An exchange anisotropic coupling on the film boundary surface betweenthe first antiferromagnetic layer 10 and the free magnetic layer 3 putsthe free magnetic layer 3 into a single-domain state in the X direction,orientating the directions of magnetization of the free magnetic layer 3in the X direction. For this reason, the first antiferromagnetic layer10 is made of a material that an exhibits exchange anisotropic couplingwith the free magnetic layer 3. In the case of the structure shown inFIG. 1, however, the first antiferromagnetic layer 10 is created firstand the free magnetic layer 3 is created thereon. For this reason, it isnecessary to make the first antiferromagnetic layer of a material, thesurface of which is not prone to corrosion after the layer is created.This is because, if the surface of the first antiferromagnetic layer 10corrodes, the close adherence between the first antiferromagnetic layer10 and the free magnetic layer 3 deteriorates. It is therefore desirableto make the first antiferromagnetic layer 10 of one of α—Fe₂O₃ (ironoxide), NiO (nickel oxide), an Ni—Mn (nickel-manganese) alloy or a Pt—Mn(platinum-manganese) alloy, a material which exhibits an exchangeanisotropic coupling with the free magnetic layer 3 and is not prone tocorrosion.

In addition, in the case of the first antiferromagnetic layer 10 made ofα—Fe₂O₃, not only does the first antiferromagnetic layer 10 provide anexchange anisotropic magnetic field Hex to the free magnetic layer 3,but the coercive force Hc of the free magnetic layer 3 created on thefirst antiferromagnetic layer 10 can also be increased. As a result, thedirection of the magnetization of the free magnetic layer 3 on the trackwidth Tw can be stabilized, allowing the amount of Barkhausen noise tobe reduced. On the top of that, at portions of offset lengths (a) and(b) on both the sides of the track width Tw, the exchange anisotropicmagnetic field Hex provided to the free magnetic layer 3 by the firstantiferromagnetic layers 10, which are made of α—Fe₂O₃, increases, andin addition, the coercive force Hc of the free magnetic layer 3 atportions closely adhered to the first antiferromagnetic layers 10 alsoincreases as well. As a result, at the portions of the offset lengths(a) and (b), the magnetization of the free magnetic layer 3 is fixed inthe X direction. In this state, the direction of the magnetization ofthe free magnetic layer 3 is hardly affected by a leaking magnetic fieldfrom the magnetic recording medium, improving the off-track performance.

It should be noted that, at the portion of the track width Tw, the freemagnetic layer 3 can be created directly above the lower-gap layer 1. Itis desirable, nonetheless, to create a nonmagnetic underlayer 2 made ofa nonmagnetic material such as Ta (tantalum) on the lower-gap layer 1and then to create the free magnetic layer 3 on the nonmagneticunderlayer 2. The nonmagnetic underlayer 2 has a bcc structure(body-centered-cubic structure) and the free magnetic layer 3 is createdon the nonmagnetic underlayer 2 to form crystal orientation, allowing afunction for reducing the relative electrical resistance of the freemagnetic layer 3 to be exhibited.

A nonmagnetic electrically conductive layer 5, a pinned magnetic layer 6and a second antiferromagnetic (pinning) layer 7 are then stacked on thefree magnetic layer 3 one after another in the order the layers 5, 6 and7 are enumerated. The nonmagnetic electrically conductive layer 5 istypically made of Cu (Copper). Much like the free magnetic layer 3, onthe other hand, the pinned magnetic layer 6 is made of the Ni—Fe alloy.As for the second antiferromagnetic layer 7, any of a Pt—Mn(Platinum-manganese) alloy, an Fe—Mn (iron-manganese) alloy or the Ni—Mn(nickel-manganese) alloy can be used. An exchange anisotropic couplingon the film boundary surface between the second antiferromagnetic layer7 and the pinned magnetic layer 6 puts the pinned magnetic layer 6 intoa single-domain state in the Y direction, fixing the directions ofmagnetization in the Y direction (a direction perpendicular to thesurface of the paper away from the reader).

An upper layer 8 which is typically made of Ta is created on the secondantiferromagnetic layer 7. Lead layers (electrically conductive layers)9 are created on the upper layer 8, sandwiching an open lead track width(Lead Tw). The lead layers 9 are each typically made of an electricallyconductive material such as Cu, Ta or W (tungsten). An upper-gap layer11 which is typically made of Al₂O₃ is then created above the upperlayer 8 and the lead layers 9.

Next, another structure of the magnetoresistive sensor shown in FIG. 2is explained.

In the case of the magnetoresistive sensor shown in FIG. 2, the firstantiferromagnetic layer 10 is created over the entire upper surface ofthe lower-gap layer 1. The nonmagnetic underlayer 2, which is typicallymade of Ta, is created at the portion of the track width Tw on the firstantiferromagnetic layer 10 such that upper surfaces of first and secondportions of the antiferromagnetic layer 10 are exposed on opposite sidesof the nonmagnetic underlayer 2. Then, the free magnetic layer 3 iscreated with first and second sections respectively formed on theexposed upper surfaces of the first antiferromagnetic layer 10 and athird section connecting the first and second sections which is formedon the nonmagnetic underlayer 2. Furthermore, the nonmagneticelectrically conductive layer 5, the pinned magnetic layer 6 and thesecond antiferromagnetic layer 7 are stacked on the free magnetic layer3 one after another in the order the layers 5, 6 and 7 are enumerated.

Much like the magnetoresistive sensor shown in FIG. 1, in themagnetoresistive sensor shown in FIG. 2, the first antiferromagneticlayer 10 is made of α—Fe₂O₃ , NiO, the Ni—Mn alloy or the Pt—Mn alloy.The second antiferromagnetic layer 7 is made of the Pt—Mn alloy, theFe—Mn alloy or the Ni—Mn alloy. The free magnetic layer 3 and the pinnedmagnetic layer 6 are, on the other hand, made of the Ni—Fe alloy. Thenonmagnetic electrically conductive layer 5 is typically made of Cu.

The first antiferromagnetic layer 10 puts the free magnetic layer 3 in asingle-domain state in the X direction, orientating the directions ofmagnetization of the free magnetic layer 3 in the X direction. On theother hand, an exchange anisotropic coupling on the film boundarysurface between the second antiferromagnetic layer 7 and the pinnedmagnetic layer 6 puts the pinned magnetic layer 6 into a single-domainstate in the Y direction, fixing the directions of magnetization in theY direction (a direction perpendicular to the surface of the paper awayfrom the reader).

The upper layer 8 which is typically made of Ta is created on the secondantiferromagnetic layer 7. The lead layers 9 are created on the upperlayer 8, sandwiching a lead track width (Lead Tw). The upper-gap layer11 is then created above the upper layer 8 and the lead layers 9.

In both the magnetoresistive sensors shown in FIGS. 1 and 2, on both thesides of the track width Tw, first and second spaced-apart portions ofthe antiferromagnetic layer 10 are closely adhered to the lower surfaceof the free magnetic layer 3. The directions of magnetization of thefree magnetic layer 3 are orientated in the X direction by an exchangeanisotropic magnetic field Hex of the first antiferromagnetic layer 10.On the other hand, the directions of magnetization of the pinnedmagnetic layer 6 are orientated by the second antiferromagnetic layer 7in a direction perpendicular to the surface of the paper away from thereader. A steady-state current is supplied from the lead layer 9 to thefree magnetic layer 3, the nonmagnetic electrically conductive layer 5and the pinned magnetic layer 6 in the X direction. When a magneticfield from the magnetic recording medium is provided in the Y direction,the direction of magnetization of the free magnetic layer 3 changes fromthe X direction to the Y direction. The change in relation between thedirection of magnetization in the free magnetic layer 3 and thedirection of magnetization of the pinned magnetic layer 6 which changeis caused by a variation in magnetization direction in the free magneticlayer 3 changes the electrical resistance of the magnetoresistivesensor. The change in electrical resistance results in a change involtage for the steady-state current which voltage change is used fordetecting the magnetic field from the magnetic recording medium.

In both the magnetoresistive sensors shown in FIGS. 1 and 2, the firstand second antiferromagnetic layers 10 and 7 are provided at locationswhich are separated from each other so that the first and secondantiferromagnetic layers 10 and 7 do not affect each other. As a result,it is easy to orientate the directions of magnetization of the freemagnetic layer 3 and the pinned magnetic layer 6 in directions which areperpendicular to each other.

The magnetization of the pinned magnetic layer 6 is fixed in the Ydirection by an exchange anisotropic coupling on the film boundarysurface between the pinned magnetic layer 6 and the secondantiferromagnetic layer 7 which is created over the entire surface ofthe pinned magnetic layer 6. In addition, in the case of the firstantiferromagnetic layer 10 made of α—Fe₂O₃ , not only the firstantiferromagnetic layer 10 provides an exchange anisotropic magneticfield Hex to the free magnetic layer 3 created thereon, but the coerciveforce Hc of portions of the free magnetic layer 3 closely adhered to thefirst antiferromagnetic layer 10 can also be increased. As a result, thedirection of magnetization of the free magnetic layer 3 on portionsother than the track width Tw in the X direction can be stabilized andsince the magnetization of portions of the offset lengths (a) and (b) ishardly affected by the external magnetic field, the off-trackperformance is excellent.

In addition, the electrical resistance of the magnetoresistive sensor asa whole is determined by the lead track width (Lead Tw). As a result, bysetting the gap between the lead layers 9 with a high degree ofaccuracy, variations in electrical resistance of the magnetoresistivesensor as a whole against a steady-state current become small.

Next, methods of manufacturing the magnetoresistive sensors shown inFIGS. 1 and 2 are explained.

Processes of manufacturing the magnetoresistive sensor shown in FIG. 1are described as follows.

{circle around (1)} The nonmagnetic underlayer 2 is created on thelower-gap layer 1 by means of a sputtering technique. Then, the uppersurface of the nonmagnetic underlayer 2 is coated with a resist materialprior to exposure and development processes. The resist layer is createdonly on the portion of the track width Tw. The track width Tw is set bythis resist layer. Then, by means of an etching technique such as ionmilling, the nonmagnetic underlayer 2 and part of the lower-gap layer 1of areas where the resist layer are not created, that is, on both thesides of the track width Tw, are removed.

{circle around (2)} With the resist layer created on the nonmagneticunderlayer 2, the first antiferromagnetic layers 10 are created by usinga sputtering technique on the lower-gap layer 1 on both sides.Thereafter, the resist layer is removed by means of an etch-back method.

{circle around (3)} The surfaces of the first antiferromagnetic layers10 and the nonmagnetic underlayer 2 are cleaned by using a reversesputtering technique. Then, the free magnetic layer 3, the nonmagneticelectrically conductive layer 5, the pinned magnetic layer 6, the secondantiferromagnetic layer 7 and the upper layer 8 are created continuouslyone after another using a sputtering technique.

{circle around (4)} A resist layer is created on the portion of the leadtrack width (Lead Tw) on the upper layer 8. With the resist layer put inits state as it is, the leads 9 are created. Then, the resist layer isremoved. In this way, the leads layers 9 are created on the upper layer8, sandwiching a gap, that is, the lead track width (Lead Tw).Thereafter, the upper-gap layer 11 is created on the upper surfaces ofthe upper layer 8 and the lead layers 9.

The magnetoresistive sensor shown in FIG. 1 can be manufactured throughthe processes described above. In these manufacturing processes, aresist layer is created on the nonmagnetic underlayer 2 in order to setthe track width Tw. By means of ion milling, portions of the nonmagneticunderlayer 2 and part of the lower-gap layer 1 are removed and the firstantiferromagnetic layers 10 are then created. Thereafter, layers fromthe free magnetic layer 3 to the upper layer 8 are created continuouslyone after another without etching. In this way, the film makingprocesses can be made simple. In addition, processes for theconventional magnetoresistive sensor shown in FIG. 3 to remove thinlayers by means of etching are not required.

In the processes of manufacturing the magnetoresistive sensor shown inFIG. 1, at a point of time after the upper layer 8 has been created, thelead track width (Lead Tw) is set by another resist layer. Asalternative subsequent processes, on both the sides of the lead trackwidth (Lead Tw), layers from the upper layer 8 to the free magneticlayer 3 or to portions of the surfaces of the first antiferromagneticlayers 10 are etched by means of ion milling and the lead layers 9 arethen created on the antiferromagnetic layers 10 on both the sides of thelead track width (Lead Tw). In this case, even though the number ofetching steps using the ion milling-technique increases, the depthaccuracy of the etching processes using the ion-milling technique is notrequired because the first antiferromagnetic layers 10 and the freemagnetic layer 3 are already closely adhered to each other. For example,even if some of the free magnetic layer 3 is left on the firstantiferromagnetic layer 10 and the lead layer 9 is created thereon, nofunctional problem arises.

Processes of manufacturing the magnetoresistive sensor shown in FIG. 2are explained as follows.

{circle around (1)} The first antiferromagnetic layer 10 is created overthe entire surface of the lower-gap layer 1 using a sputteringtechnique. Subsequently, the nonmagnetic underlayer 2 is created on thefirst antiferromagnetic layer 10 also using a sputtering technique.Then, a resist layer for setting the track width Tw is created on thenonmagnetic underlayer 2. Subsequently, the nonmagnetic underlayer 2 anda portion of the antiferromagnetic layer 10 in areas where the resistlayer is not created are removed by an etching technique such as ionmilling.

{circle around (2)} Thereafter, layers from the free magnetic layer 3 tothe upper layer 8 are continuously created one after another. By thesame token, the lead layers 9 and the upper-gap layer 11 are created.

As described above, in the case of the method of manufacturing themagnetoresistive sensor shown in FIG. 1, the nonmagnetic underlayer 2and the lower-gap layer 1 are removed by an etching technique such asion milling. The etching depth does not have an effect on themagnetoresistive sensor. Also in the case of the method of manufacturingthe magnetoresistive sensor shown in FIG. 2, the functions of themagnetoresistive sensor are not affected even if an error is generatedin the etching depth for the first antiferromagnetic layer 10. Inaddition, at the point of time the free magnetic layer 3 is created, thefree magnetic layer 3 and the first antiferromagnetic layer 10 areclosely adhered to each other with a high degree of reliability on boththe sides of the track width Tw. As a result, the manufacturing methodsbecome simple. In addition, the directions of magnetization in the freemagnetic layer 3 of the magnetoresistive sensor after the manufacturingare orientated in one direction with a high degree of reliability andthe amount of the Barkhausen noise is also reduced as well.

As described above, in both the magnetoresistive sensors shown in FIGS.1 and 2, the second antiferromagnetic layer 7 is used for putting thepinned magnetic layer 6 in a single-domain state in the Y direction. Itshould be noted that, as an alternative, a magnetic material with alarge coercive force Hc can be created on the pinned magnetic layer 6and the permanent magnetization of the magnetic material is used fororientating the directions of magnetization in the pinned magnetic layer6 in the Y direction.

According to the present invention, the antiferromagnetic layer formagnetizing the free magnetic layer in one direction is closely adheredto the lower surface of the free magnetic layer. In this way, the freemagnetic layer and the antiferromagnetic layer are adhered to each otherwith a high degree of reliability, allowing the direction ofmagnetization of the free magnetic layer to be stabilized. Inparticular, in the case of an antiferromagnetic layer made of α—Fe₂O₃ ,the magnetization of the free magnetization layer at portions other thanthe track width is stabilized, improving the off-track performance.

Unlike the conventional magnetoresistive sensor, the number of processesto etch layers can be reduced, making it possible to make themanufacturing processes simple. In addition, unlike the conventionalmagnetoresistive sensor, the state of adherence of the free magneticlayer and the antiferromagnetic layer is not affected by the etchingaccuracy and, at the time the free magnetic layer is created, the freemagnetic layer and the antiferromagnetic layer can be adhered to eachother with a high degree of reliability.

What is claimed is:
 1. A magnetoresistive sensor comprising: lower-gap layer having an upper surface; a first antiferromagnetic layer formed over the lower-gap layer, the first antiferromagnetic layer including first and second portions, each of the portions having an upper surface, the upper surface of the first portion being separated alone a first direction from the upper surface of the second portion, and extending over the upper surface of the lower gap layer in said first direction; a free magnetic layer including first and second sections respectively formed on the upper surfaces of the first and second portions of the first antiferromagnetic layer, the free magnetic layer having a third section extending between the first and second sections, a direction of magnetization of the free magnetic layer being oriented through exchange anisotropic coupling with the first and second potions of the first antiferromagnetic layer; a nonmagnetic electrically conductive layer formed on the free magnetic layer, a pinned magnetic layer formed on the nonmagnetic electrically conductive layer; and a second antiferromagnetic layer formed on the pinned magnetic layer for pinning a direction of magnetization of the pinned magnetic layer through exchange anisotropic coupling such that the pinned direction of magnetization crosses the oriented direction of magnetization of the free magnetic layer, wherein the electrical resistance of the magnetoresistive sensor varies when the oriented direction of magnetization of the free magnetic layer is changed by an external magnetic field, wherein the lower-gap layer includes first and second removed portions and an upper surface extending between the first and second removed portions, wherein the first and second portions of the first antiferromagnetic layer are respectively formed in the first and second removed portions, and the free magnetic layer is formed on the upper surfaces of the first and second portions of the first antiferromagnetic layer and on the upper surface of the lower-gap layer located between the first and second portions of the first antiferromagnetic layer.
 2. A magnetoresistive sensor according to claim 1, wherein the first antiferromagnetic layer comprises a material selected from the group consisting of α—Fe₂O₃ (iron oxide), NiO (nickel oxide), Ni—Mn (nickel-manganese) alloy and Pt—Mn (platinum-manganese) alloy.
 3. A magnetoresistive sensor comprising: a lower-gap layer having an upper surface; a first antiferromagnetic layer formed over the lower-gap layer, the first antiferromagnetic layer including first and second portions, each of the portions having an upper surface, the upper surface of the first portion being separated along a first direction from the upper surface of the second portion, and extending over the upper surface of the lower gap layer in said first direction; a free magnetic layer including first and second sections respectively formed on the upper surfaces of the first and second portions of the first antiferromagnetic layer, the free magnetic layer having a third section extending between the first and second sections, a direction of magnetization of the free magnetic layer being oriented through exchange anisotropic coupling with the first and second potions of the first antiferromagnetic layer; a nonmagnetic electrically conductive layer formed on the free magnetic layer, a pinned magnetic layer formed on the nonmagnetic electrically conductive layer; and a second antiferromagnetic layer formed on the pinned magnetic layer for pinning a direction of magnetization of the pinned magnetic layer through exchange anisotropic coupling such that the pinned direction of magnetization crosses the oriented direction of magnetization of the free magnetic layer, wherein the electrical resistance of the magnetoresistive sensor varies when the oriented direction of magnetization of the free magnetic layer is changed by an external magnetic field, wherein a nonmagnetic layer is formed on the first antiferromagnetic layer, the nonmagnetic layer being located between the first and second portions, and wherein the third section of the free magnetic layer is formed on an upper surface of the nonmagnetic layer.
 4. A magnetoresistive sensor according to claim 3, wherein the first antiferromagnetic layer comprises a material selected from the group consisting of α—Fe₂O₃ (iron oxide), NiO (nickel oxide), Ni—Mn (nickel-manganese) alloy and Pt—Mn (platinum-manganese alloy.
 5. A magnetoresistive sensor comprising: an undivided, aluminum oxide insulating layer; a first antiferromagnetic layer overlying the insulating layer and having first and second sections, wherein the first and second sections are separated by a surface region of the insulating layer; a free magnetic layer overlying and in intimate contact with an upper surface of the first and second sections; and a pinned magnetic layer overlying the free magnetic layer; and a nonmagnetic electrically conductive layer interposed between the free magnetic layer and the pinned magnetic layer; a second antiferromagnetic layer overlying the pinned magnetic layer wherein the free magnetic layer is interposed between the nonmagnetic electrically conductive layer and the first antiferromagnetic layer, and wherein the pinned magnetic layer is interposed between the nonmagnetic electrically conductive layer and the second antiferromagnetic layer.
 6. The sensor of claim 5, wherein the first antiferromagnetic layer comprises a material selected from the group consisting of α—Fe₂O₃ (alpha iron oxide), NiO (nickel oxide), NiMn (nickel manganese) alloy, and Pt—Mn (platinum-manganese) alloy.
 7. The sensor of claim 5, wherein the antiferromagnetic layer comprises nickel oxide.
 8. The sensor of claim 5, further comprising a nonmagnetic layer overlying the surface region of the insulating layer and separating the free magnetic layer therefrom.
 9. The sensor of claim 5, wherein the surface region comprises a region having a lateral distance proportional to a track width.
 10. The sensor of claim 5, wherein the second antiferromagnetic layer comprises a material selected from the group consisting of an iron-manganese alloy, a nickel-manganese alloy, and a platinum-manganese alloy.
 11. A magnetoresistive sensor comprising: an insulating layer having first and second recessed regions; an antiferromagnetic layer comprising a first antiferromagnetic layer section in contact with the first recessed region and a second antiferromagnetic layer section in contact with the second recessed region, the second antiferromagnetic layer section disposed in substantially the same plane as the first antiferromagnetic layer section and separated from the first antiferromagnetic layer section by the insulating layer to define a track width region between the first and second antiferromagnetic layer sections; a pinned magnetic layer; a pinning layer pinning the pinned magnetic layer; a free magnetic layer interposed between the pinned magnetic layer and the antiferromagnetic layer; a nonmagnetic electrically conductive layer interposed between the pinned magnetic layer and the free magnetic layer.
 12. A magnetoresistive sensor according to claim 11, wherein the pinning layer is formed in contact with said pinned magnetic layer, and wherein said pinned magnetic layer is interposed between said nonmagnetic electrically conductive layer and said pinning layer.
 13. A magnetoresistive sensor comprising: an insulating layer; a first antiferromagnetic layer overlying the insulating layer and having first and second sections, wherein the first and second sections are separated by a surface region of the insulating layer; a nonmagnetic layer overlying the upper surface region of the insulating layer; a free magnetic layer overlying and in intimate contact with an upper surface of the first and second sections and an upper surface of the nonmagnetic layer; and a pinned magnetic layer overlying the free magnetic layer; and a nonmagnetic electrically conductive layer interposed between the free magnetic layer and the pinned magnetic layer; a second antiferromagnetic layer overlying the pinned magnetic layer wherein the free magnetic layer is interposed between the nonmagnetic electrically conductive layer and the first antiferromagnetic layer, and wherein the pinned magnetic layer is interposed between the nonmagnetic electrically conductive layer and the second antiferromagnetic layer.
 14. The sensor according to claim 13, wherein the first antiferromagnetic layer comprises a material selected from the group consisting of α—Fe₂O₃ (alpha iron oxide), NiO (nickel oxide), NiMn (nickel manganese) alloy, and Pt—Mn (platinum-manganese) alloy.
 15. The sensor according to claim 13, wherein the antiferromagnetic layer comprises nickel oxide.
 16. The sensor according to claim 13, wherein the surface region comprises a region having a transverse distance proportional to a track width.
 17. The sensor according to claim 13, wherein the second antiferromagnetic layer comprises a material selected from the group consisting of iron-manganese alloy, nickel-manganese alloy, and platinum-manganese alloy.
 18. The sensor according to claim 13, wherein the nonmagnetic layer comprises tantalum (Ta). 